Hitherto, as a vibration damping material for substrates such as steel articles for cars, washing machines, and various other kinds of substrates, various kinds of metal articles, synthetic resin plates, etc., a sheet-form material has generally been used and such a sheet-form material has been applied to the base plate by fusion welding. However, since, for example, the floor of a car, etc., usually has a complicated form, it is difficult to coat the whole surface of the floor and there is the difficulty that a partial inferior adhesion occurs at portions which have not been welded, whereby a sufficient vibration damping property is not obtained.
It is necessary that a vibration damping material for the interior of a car has sufficient fluidity at coating for increasing the working efficiency of the automation of a process line and also has the property of not sagging even in the case of applying a thick coating of about 5 mm. Further, it is required that the vibration damping material has good adhesion to substrates such as steel plates, etc., even under severe vibration or shock, and also is light in weight.
As a method of solving such problems, a method of coating a vibration ,damping material having a filler has been proposed as described, e.g., in JP-A-55-58262 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Also, the inventors preciously provided a vibration damping coated film-forming material excellent in adhesion, working properties, and vibration damping property, as described in JP-A-62-227966.
However, such conventional vibration damping coated film-forming materials have disadvantages in the points of adhesion, working properties, etc.
Further, recently, the development of a vibration damping coated film-forming material having a lower specific gravity (i.e., which is light in weight) has been desired.
A coating composition is typically a mixture of various fillers, a high molecular weight resinous material and an organic solvent as a diluent and such a coating composition is coated on a material using various kinds of coating methods.
The organic solvent as a diluent normally has high volatility, creates the danger of fire, and has high toxicity, whereby the organic solvent cause the problem of environmental pollution upon volatilizing the same.
Thus, recently, water base coating compositions using water in place of an organic solvent have been developed.
Water base coating compositions are generally classified into emulsion coating compositions (aqueous dispersion coating compositions) and water-soluble resin coating compositions. In these coating compositions, no organic solvent is used as a diluent or if an organic solvent is used, the amount thereof is very low.
To shorten the drying time of a water base coating composition as described above, drying with a hot air stream of a temperature of about 100.degree. C. is generally employed. The foregoing film-forming coating composition previously proposed by the inventors herein is coated and dried with an air stream in the temperature range of from room temperature to 180.degree. C.
However, the foregoing coating composition previously proposed by the inventors herein is subject to the following problem.
At a relatively high drying temperature of higher than 60.degree. C. for a coated film or layer formed using the foregoing coating composition (practically, in the temperature range of from room temperature to 180.degree. C.), sometimes the coated film formed by coating the coating composition blisters and it is difficult to always obtain a good coated film or layer.
The reason for this is considered to be as follows. When the coated film is dried at a temperature higher than 60.degree. C. and, in particular, when the thickness of the coated layer is thicker than that formed using a conventional coating composition, drying of the coated film occurs from the surface thereof and water confined in the interior of the coated film expands without being evaporated to cause blistering in the coated film.
When blistering occurs on the surface of the coated film or layer, not only is the appearance of the film or layer spoiled, but also the performance required for the coated film, such as a vibration damping property, adhesion, etc., is not sufficiently obtained, which results in a lowering of the commercial value of the coated article.
Accordingly, it is necessary to dry such a coated film at a relatively low temperature of not higher than 60.degree. C. or to reduce the thickness of the coated film.
However, in the case of drying at a low temperature, the coating procedure is prolonged, which reduces the efficiency of the production step for the product.
In the case of forming a thin coated film, there are restrictions on the use of such a thin film or layer. Also, if a desired greater thickness of the coated film is required, the steps of coating a thin coated film and drying and then further coating another thin coated film followed by drying must be repeated several times, which results in prolonging the coating procedure and further causing the problem of peeling of each coated film.